Everton signed forward Ramirez from Spanish club Malaga in the summer transfer window for a fee reported by Sky Sports to be worth £5.25 million.
The Premier League club also recruited forward Vlasic from Hajduk Split for a transfer fee reported by BBC Sport to be worth £10m.
Former Arsenal star Merson has asked whether the 22-year-old and the 19-year-old would be able to score 15 goals between them this season.
While suggesting that Everton should have signed France international striker Olivier Giroud from Arsenal in the summer transfer window, Merson told Sky Sports: “I don’t see how he (Giroud) wouldn't have got 15 goals. To go with Sandro and the other lad (Vlasic), would they get 15 between them this season?”
Everton lost one of the best strikers in the Premier League in Romelu Lukaku to Premier League rivals Manchester United in the summer transfer window.
The Belgium international striker is a proven goalscorer, and it will be interesting to see how the Toffees compensate for his goals this season.
Ronald Koeman’s side will take on Manchester United at Old Trafford in the Premier League on Sunday afternoon.